Vibrio cholerae is the causative agent of cholera, an acute life-threatening diarrhea disease. Cholera epidemics occur with seasonal regularity in endemic areas, such as the Ganges Delta region of South Asia. Cholera epidemics in 2010 in Africa, Pakistan, and Haiti remind us that further investigation of this disease is warranted. The ability of V. cholerae strains to cause severe enteric infection in humans depends on their virulence gene content. Bacterial viruses infecting Vibrio species (vibriophages/phages) are known to play a critical role in the transmission of the virulence genes among different strains of V. cholerae (e.g., cholera toxin genes via the filamentous phage CTXf). Furthermore, our fieldwork in Bangladesh has provided direct evidence that lytic vibriophages seemly end cholera epidemics through predation and influencing infectivity. The objective of this proposal is to learn how vibriophages drive the emergence of new pathogenic clones of V. cholerae through horizontal gene transfer, predation, and other biological interactions that affect properties such as biofilm formation, infectivity and environmental persistence. We will approach this problem with six specific aims 1) we will attempt to reconstruct the chromosomal arrangement of filamentous prophages found in the 7th pandemic strain, the most successful clone of toxigenic V. cholerae; 2) we will study the formation of hybrid filamentous phages encoding virulence properties and different host range; 3) we will use comparative genome sequence analysis of both phages and V. cholerae isolates to deduce the mechanisms of phage- resistance and displacement phages in Bangladesh aquatic environment; 4) we will utilize biofilm-degrading phages to study the effect of biofilm dissociation on V. cholerae infectivity and persistence in th environment; 5) we will test the ability of phages to mediate transfer of virulence genes or to produce virulence factors such as inflammatory molecules, cytotoxins and enterotoxins; 6) we will construct genetically marked phages suitable for environmental release and accurate subsequent molecular tracking in water and patients.